HLA typing was performed on lymphocytes from patients with a common disease or families in which more than one member shared the same disease. Subpopulations of patients with Sjogren's syndrome as well as families with this disease and with additional different autoimmune conditions demonstrated specific HLA-DR antigen combinations in each autoimmune subset. In families with Hodgkin's disease, homozygosity at the HLA-DR MT1 locus more frequently occurred in the diseased individuals than in the nondiseased family members. Families of patients with adult T-cell leukemia (ATL), including individuals with antiviral antibodies, demonstrated HLA linkage, with a lode score of 2.5. HLA typing of AIDS (predominantly Kaposi's sarcoma) demonstrated an increased frequency of the HLA-DR5 antigen as well as HLA-DR MT2. Expression of HLA-A,B,C and HLA-DR was studied and compared in established cell lines from patients with adult T-cell lymphocytic leukemia (T-ALL) and HTLV-I-associated adult T-cell leukemias. No differences between the two diseases in DNA methylation were observed for the HLA-A,B,C antigens. HLA-DR, however, was highly methylated in the T-ALLs and only partially methylated in the HLA-DR-expressing ATL cell lines. Using fresh cells from patients (HLA-DR negative) with ATL, this same pattern of methylation was observed. After short-term culture (48 hours), HLA-DR was expressed on the cell surface, and no differences in the methylation patterns were observed. The results suggest a post-transcriptional control (in certain instances) for the expression of HLA-DR antigens. Expression of HLA-DR was studied in cord blood lymphocytes. It was observed that these monocytes, in contrast to adult monocytes, express low levels of HLA-DR. These cells could be induced to express these determinants with various lymphokines and gamma-interferon. Cytotoxic T cells were generated to autologous HTLV-infected cells. Cytotoxicity of these cells was restricted to other HTLV-infected cell lines that shared the HLA-A1 determinant.